In the field of LSIs, the required diameter for silicon single crystals has been increased year after year. At present, crystals of 6 inches in diameter are used for the latest devices. It is said that in the future crystals of 10 inches or over in diameter, e.g., crystals of 12 inches in diameter will be needed.
In accordance with the Czochralski method (CZ method) which is known as a method of manufacturing large-diameter silicon single crystals, the amount of molten silicon in a crucible is decreased as a single crystal is grown. As a result, the dopant concentration is increased and the oxygen concentration is decreased in the crystal as the crystal is grown. In other words, the properties of the crystal are varied in the direction of its growth. Since the quality required for silicon single crystals has been made severer year after year with increase in the level of integration of LSIs, this problem must be overcome.
As a means of solving this problem, a method has been known from the old in which the interior of a quartz crucible according to the ordinary Czochralski method is divided by a quartz crucible having small holes for molten silicon so that the inner side forms a single crystal growing section and the outer side forms a material melting section thereby growing a cylindrical silicon single crystal on the inner side while continuously feeding starting material silicon to the material melting section, and many patents have been disclosed (Patent Publication No. 40-10184, Laid-Open Patent No. 62-241889, Laid-Open Patent No. 63-233092, Laid-Open Patent No. 63-319287, Laid-Open Patent No. 64-76992 and Laid-Open Patent No. 1-96087).
Where a silicon single crystal is manufactured by use of a double structure crucible incorporating therein a partition member on the basis of the prior art technique such as described above, however, the heat environment in the molten silicon is the very opposite to that in cases in which the ordinary single structure crucible without any partition member is used.
FIGS. 9 and 10 are longitudinal section views respectively showing the cases of the above-mentioned single structure crucible and double structure crucible. In the Figures, numeral 21 designates a crucible, 22 a partition, 4 molten silicon, 5 a pulled silicon single crystal, and 12 small holes formed through the partition 22 for molten silicon. Also, arrows show the directions of the convection of molten silicon. In the case of FIG. 9, the crucible side wall portion is higher in temperature than the crucible bottom portion. In other words, the amount of heat supplied through the crucible side wall portion is greater than the amount of heat supplied through the crucible bottom portion. Reflecting this fact, the convection of the molten silicon within the quartz crucible 21 is predominated by the flows indicated by the arrow in FIG. 9. In the case of FIG. 10, however, the amount of heat supplied to the single crystal growing section through the crucible side is such that the proportion of the heat input through the bottom portion of the crucible 21 is increased as compared with the case of FIG. 9. This is due to the fact that the side portion of the partition 22 is remote from the heat source and the temperature distribution in the molten silicon 4 of the material melting section is higher in temperature in the bottom portion than in the remainder. In such heat environment where the proportion of the heat input through the bottom portion is great, there is a tendency that the heat convection of the molten silicon within the single crystal growing section is predominated by the convection as shown in FIG. 10 which is the very opposite to FIG. 9. In the case of such convection, the high-temperature molten silicon in the bottom portion of the crucible 21 is directly moved to the solid-liquid interface of a silicon single crystal and therefore there is caused a problem that the stable pulling of the silicon single crystal is impeded.
The present invention has been made in view of these circumstances and it is an object of the invention to provide a silicon single crystal manufacturing apparatus which employs a double structure crucible having a partition member so that high-temperature molten silicon in the bottom portion of the crucible is not moved to the solid-liquid interface and the stable pulling of a silicon single crystal is ensured.